EVALUATION OF THE PROXIMAL FLOW-FIELD TO CIRCULAR AND NONCIRCULAR ORIFICES OF DIFFERENT ASPECT RATIOS

Investigations of valvular regurgitation attempt to specify flow field characteristics and apply them to the proximal isovelocity surface ar ea (PISA) method for quantifying regurgitant flow. Most investigators assume a hemispherical shape to these equivelocity shells proximal to an axisymmetric (circular) orifice. However, in vivo flow fields are v iscous and regurgitant openings vary in shape and size. By using cente rline profiles and isovelocity surfaces, this investigation describes the flow field proximal to circular and elliptical orifices. Steady, p roximal flow fields are obtained with two-and three-dimensional comput ational fluid dynamic (CFD) simulations. These simulations are verifie d by in vitro, laser-Doppler velocimetry (LDV) experiments. The data s how that a unique, normalized proximal flow field results for each ori fice shape independent of orifice flow or size. The distinct differenc es in flow field characteristics with orifice shape may provide a mech anism for evaluating orifice characteristics and regurgitant flows. In stead of the hemispherical approximation technique, this study attempt s to show the potential to define a universal flow evaluation method b ased on the details of the flowfield according to orifice shape. Preli minary results indicate that Magnetic Resonance (MR) and Color Doppler (CD) may reproduce these flow details and allow such a procedure in v ivo.